Differential thermistor circuit

ABSTRACT

This document discusses, among other things, an apparatus and method for providing temperature information. In an example, an integrated circuit apparatus can include a first resistor configured to be coupled to a first terminal of a temperature-sensitive resistance, a second resistor configured to be coupled to a second terminal of the temperature-sensitive resistance, and a temperature information circuit configured to receive a first voltage from the first terminal of the temperature-sensitive resistance and a second voltage from the second terminal of the temperature-sensitive resistance. The temperature information circuit can provide the temperature information using the first and second voltages.

CLAIM OF PRIORITY

This application is a divisional application of U.S. patent applicationSer. No. 13/014,317, filed Jan. 26, 2011, entitled DIFFERENTIALTHERMISTOR CIRCUIT, now U.S. Pat. No. 8,727,616, which claims thebenefit of priority under 35 U.S.C. 119(e) of U.S. Provisional PatentApplication Ser. No. 61/325,634, filed on Apr. 19, 2010, each of whichis incorporated herein by reference in its entirety.

BACKGROUND

A resistor is a two-terminal electronic component that produces avoltage across the terminals proportional to the current passing throughthem. Ohm's law defines the value of the resistor as the ratio of thevoltage produced across the terminals to the current passing throughthem. A thermistor is a type of resistor whose resistance changes withtemperature. Accordingly, the voltage across the terminals of thethermistor varies with the temperature and the current passing throughthem.

OVERVIEW

This document discusses, among other things, an apparatus and method forproviding an indication of temperature using first and second voltagesfrom first and second terminals of a thermistor, including providing afirst resistor configured to be coupled to the first terminal of thethermistor and a second resistor configured to be coupled to the secondterminal of the thermistor.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIGS. 1A-1C illustrate generally examples of single-ended thermistorinformation, including a thermistor voltage, a filtered thermistorvoltage, and universal serial bus (USB) data.

FIG. 2 illustrates generally an example of a differential thermistorcircuit.

FIG. 3 illustrates generally an example of a differential thermistorprocessing circuit.

FIG. 4 illustrates generally an example of an alternative differentialthermistor processing circuit.

FIG. 5 illustrates generally an example of an alternative differentialthermistor processing circuit.

DETAILED DESCRIPTION

The present inventors have recognized, among other things, an integratedthermistor sense circuit configured to differentially sense a voltageacross an external thermistor for comparison with a reference voltage.In an example, the reference voltage can be determined using a resistor,such as a resistor external to the integrated thermistor sense circuit.Further, the resistance of the thermistor can be compared to a referenceresistance (e.g., the external resistor). In certain examples,differential sensing of the voltage across the thermistor can providefor enhanced signal integrity, or for the use of enhanced signalintegrity techniques, in comparison with non-differential sensing of thevoltage across the thermistor, allowing broader use in noisyenvironments.

In an example, a thermistor can be sensed in a single-ended fashion witha voltage forced across the thermistor and one or more series orparallel external resistors. In certain examples, the single-endedimplementation can be bypassed with a large capacitor to remove aportion of the noise. However, this implementation can have a high powercost and a long settling time.

FIGS. 1A-1C illustrate generally examples of single-ended thermistorinformation, including a thermistor voltage 101, a filtered thermistorvoltage 102, and universal serial bus (USB) data 103. In an example, thethermistor voltage 101 illustrates noise due to data crosstalk onto asingle-ended thermistor input. In certain examples, the thermistorvoltage can be filtered (e.g., using a large capacitor, etc.). Thefiltered thermistor voltage 102 illustrates that filtering thethermistor input can reduce the magnitude of the noise. However, thereduction can be insufficient for accurate temperature measurement. Thesource of noise can include, for example, the USB data 103, among otherthings.

In contrast, a thermistor sense circuit disclosed herein can includeequivalent or substantially equivalent impedances on the positive andnegative ends of a thermistor to reduce the level of common mode noisecoupled to a thermistor sense input. The voltage across the thermistorcan be compared to a reference resistance using a differential amplifierand a reference voltage, or the differential voltage can be converted toa ground referenced voltage, and a comparison can be made between theground referenced voltage and one or more other ground referencedvoltages.

FIG. 2 illustrates generally an example of a differential thermistorcircuit 200. In certain examples, an integrated circuit 201 includes thedifferential thermistor circuit 200. The differential thermistor circuit200 can include a voltage source 202, a first impedance 203, and asecond impedance 204. In certain examples, the first and secondimpedances 203, 204 can include respective first and second resistors.The integrated circuit 201 can include first and second terminalsterminals 205, 206 to connect the differential thermistor circuit 200 toa thermistor 207 or one or more other temperature sensitive impedances,such as a temperature sensitive resistor, etc., that, in certainexamples, can be external to the integrated circuit 201. From a circuitperspective, the thermistor 207 is coupled in series and between thefirst and second impedances 203, 204. The voltage source 202 can providea predetermined bias voltage across the series-connected first andsecond impedances 203, 204 and the thermistor 207. The voltage caninduce a current through each of the series-connected components. Acomponent voltage corresponding to the resistance and current flowthrough an individual component can be established across each of theindividual series-connected components. The first and second terminals205, 206 of the integrated circuit 201 can provide a component voltage(V_(T)) 208 that is proportional to the impedance of the thermistor 207.The impedance of thermistor 207 can indicate an ambient temperatureabout the thermistor 207.

In certain examples, the first and second impedances 203, 204 aresubstantially equal. The balanced nature of the first and secondimpedances 203, 204 can substantially reduce the effect of common modenoise at the first and second terminals 205, 206 of the integratedcircuit 201. Such a reduction in noise, without the use of a largefilter capacitor, can allow for quick and accurate temperature readingsof the voltage V_(T) 208 across the thermistor 207. In addition,substantial power savings can be realized using the circuit of FIG. 2compared to a capacitor filtered thermistor circuit because the voltagesupply need only be turned on for a short period of time to detect thevoltage V_(T) 208 across the thermistor 207. For capacitor filteredthermistor circuits, the circuit must be powered on long enough to allowthe filtering effects of the capacitor to settle out. In certainexamples, the first and second terminals 205, 206 of the integratedcircuit 201 can be coupled to other components of the integrated circuit201 and the voltage V_(T) 208 received from the thermistor 207 can beprocessed to provide temperature information.

In various examples, the voltage source 202 can include an amplifier 209and a transistor 210 arranged as a voltage follower. The amplifier 209can include an operational amplifier, and the transistor 210 can includeat least one of an NPN, PNP, NMOS, PMOS, or other transistor device. Inan example, the voltage follower can force a voltage across the firstand second impedances 203, 204 and the thermistor 207. Common mode noisecan be terminated to ground on one side of the thermistor 207 using thesecond impedance 204, and common mode noise can be terminated to an ACground on the other side of the thermistor 207 using the voltagefollower and the first impedance 203.

FIG. 3 illustrates generally an example of a differential thermistorprocessing circuit 320. In certain examples, the differential thermistorprocessing circuit 320 includes a differential thermistor circuit 300,such as the differential thermistor circuit 200 illustrated in FIG. 2,and additional components for processing information received from thethermistor 307. In certain examples, an integrated circuit 301 caninclude the differential thermistor processing circuit 320. In anexample, the differential thermistor processing circuit 320 can includea differential amplifier 321, a comparator 322 and a reference circuit323. The differential amplifier 321 can process the voltage receivedfrom the first and second thermistor terminals 305, 306 of thedifferential thermistor processing circuit 320. The reference circuit323 can provide a reference signal, V_(R), to compare with the output ofthe differential amplifier 321. The comparator 322 can compare theprocessed thermistor signal to the reference signal V_(R) and providetemperature information (TI) 330 about the thermistor 307 using therelationship between the processed thermistor signal and the referencesignal, V_(R).

In an example, the reference circuit 323 can include a voltage source,such as a voltage follower 324. The voltage follower 324 can assert avoltage across a voltage divider 325. The voltage divider 325 caninclude a plurality of resistors 326, 327. In an example, a node 329 ofthe voltage divider 325 can be coupled to the comparator 322 to providethe reference voltage, V_(R). In an example, a resistor 327 external tothe integrated circuit 301 can be one of the plurality of resistors 326,327 of the voltage divider 325. In certain examples, one or moreexternal resistors, such as external resistor 327, can be selected toprovide a programmable reference voltage to the comparator 322.

In an example, the temperature information 330 can be further processedby other circuits, such as other circuits of the integrated circuit 301,or other circuits external to the integrated circuit 301.

FIG. 4 illustrates generally an example of an alternative differentialthermistor processing circuit 420. In certain examples, an integratedcircuit 401 can include the differential thermistor processing circuit420. The differential thermistor processing circuit 420 can include adiode based differential thermistor circuit 402, a band-gap referencecircuit 423, first and second analog to digital converters (ADCs) 431,432 and a processing unit 433. The thermistor circuit 402 can provide adifferential voltage related to an ambient temperature about athermistor diode 407, such as a thermistor diode coupled externally tothe integrated circuit 401. In an example, the thermistor diode 407 canbe positioned remote from the differential thermistor processing circuit420. The differential thermistor circuit 402 can include a firstimpedance 403 coupled to one terminal of the thermistor diode 407 and asecond impedance 404 coupled to another terminal of the thermistor diode407. The first and second impedances 403, 404 can reduce the effect ofcommon mode noise on the voltage sensed across the terminals of thethermistor diode 407. In certain examples, the first and secondimpedances 403, 404 can include first and second resistors. The voltageacross the thermistor diode 407 can be converted to digital sensedinformation using the first ADC 431. A band-gap voltage generator 423can provide band-gap voltage information for processing with thethermistor diode information. An output of the band-gap voltagegenerator 423 can be converted to digital reference information usingthe second ADC 432. The processing unit 433 can process the sensedinformation and the reference information received from the first andsecond ADCs 431, 432 to generate temperature information 430 relevant tothe location of the thermistor diode 407. Such information can be usedfor a variety of applications, especially for applications susceptibleto noise, including, but not limited to, triggering temperature relatedoperation changes of devices including the integrated differentialthermistor processing circuit. Such devices include, but are not limitedto, wireless communication devices, switch devices, devices configuredto operate in extreme temperatures or which can cause extremetemperatures and can adapt operation during exposure to extremetemperatures. In certain examples, the processing unit 433 can determinea value difference between the reference information and sensedinformation. In some examples, the processed information derived fromthe reference and sensed information can be multiplied by a conversionfactor to provide temperature information 430 about the location of thethermistor diode 407. In certain examples, the processed information canbe indicative of a voltage derived from the sensed information and thereference information and the processing unit can use a conversionformula for the thermistor diode 407 to convert the voltage totemperature information 430.

In an example, the temperature information 430 can be further processedby other circuits, such as other circuits of the integrated circuit 401,or other circuits external to the integrated circuit 401.

FIG. 5 illustrates generally an example of an alternative differentialthermistor processing circuit 520. In an example, an integrated circuit501 can include the differential thermistor processing circuit. In anexample, the differential thermistor processing circuit 520 can includea diode based differential thermistor circuit 502, a diode basedreference circuit 523, first and second analog-to-digital converters531, 532 and a processing unit 533. In an example, the diode baseddifferential thermistor circuit 502 can provide a differential voltagerelated to an ambient temperature about a diode 507 connected externalto the integrated circuit 501. In some examples, the diode 507 can bepositioned remote from the integrated circuit 501. In other examples,the diode 507 can be included in the integrated circuit 501. Thedifferential thermistor circuit 502 includes a first impedance 503coupled to one terminal of the thermistor diode 507 and a secondimpedance 504 coupled to another terminal of the thermistor diode 507.The first and second impedances 503, 504 can reduce the effect of commonmode noise on the voltage sensed between the terminals of the thermistordiode 507. In certain examples, the first and second impedances 503, 504can include first and second resistors. The voltage across thethermistor diode 507 can be converted to first digital information usingthe first ADC 531. A diode based reference circuit 523 can providereference voltage information for processing with the thermistor diodeinformation.

The diode based reference circuit 523 can include a voltage follower524, and a plurality of devices to provide an reference voltageinformation to a second ADC 532. The plurality of devices can includefirst and second impedances 526, 528, and a reference diode 527. Incertain examples, the first and second impedances 526, 528 of the diodebased reference circuit 523 can include first and second resistors. Thevoltage follower can apply a bias voltage to the series-connecteddevices, first and second impedances 526, 528, and the reference diode527. The reference voltage information can include a voltage at a nodeof the reference diode 507.

In an example, an output of the diode based reference circuit 523 can beconverted to second digital information using the second ADC 532. Theprocessing unit 533 can process the digital information received fromthe first and second ADCs 531, 532 to generate temperature information530 relevant to the location of the thermistor diode 507. In someexamples, the integrated circuit 501 can include the differentialthermistor processing circuit 520 as well as other circuits. In someexamples, the temperature information 530 can be available to the othercircuits. In some examples, the temperature information 530 can beprovided at an output 534 of the integrated circuit 501. In someexamples, a digital signal includes the temperature information 530. Insome examples, an analog signal includes the temperature information530. In some examples, an analog signal and a digital signal includesthe temperature information 530. In an example, the temperatureinformation 530 can be further processed by other circuits, such asother circuits of the integrated circuit 501, or other circuits externalto the integrated circuit 501.

Additional Notes

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” All publications, patents, and patent documentsreferred to in this document are incorporated by reference herein intheir entirety, as though individually incorporated by reference. In theevent of inconsistent usages between this document and those documentsso incorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects.

The above description is intended to be illustrative, and notrestrictive. For example, although the examples above have beendescribed relating to PNP devices, one or more examples can beapplicable to NPN devices. In other examples, the above-describedexamples (or one or more aspects thereof) may be used in combinationwith each other. Other embodiments can be used, such as by one ofordinary skill in the art upon reviewing the above description. TheAbstract is provided to comply with 37 C.F.R. §1.72(b), to allow thereader to quickly ascertain the nature of the technical disclosure. Itis submitted with the understanding that it will not be used tointerpret or limit the scope or meaning of the claims. Also, in theabove Detailed Description, various features may be grouped together tostreamline the disclosure. This should not be interpreted as intendingthat an unclaimed disclosed feature is essential to any claim. Rather,inventive subject matter may lie in less than all features of aparticular disclosed embodiment. Thus, the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separate embodiment. The scope of the invention should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A method comprising: receiving a first voltage from a first resistor coupled to a first terminal of a temperature-sensitive resistance at a temperature information circuit; receiving a second voltage from a second resistor coupled to second terminal of the temperature-sensitive resistance at the temperature information circuit; providing an output signal indicative of a difference between the first and second voltages; and comparing the output signal to a reference voltage to provide an indication of temperature.
 2. The method of claim 1, wherein comparing the output signal to a reference voltage includes receiving the reference voltage from a reference resistor.
 3. The method of claim 1, wherein comparing the output signal to a reference voltage includes receiving the reference voltage from a reference diode.
 4. The method of claim 1, wherein a value of the first resistor substantially corresponds to a value of the second resistor.
 5. The method of claim 1, wherein the providing includes amplifying a difference between the first and second voltages using a differential amplifier of the temperature information circuit to provide temperature information.
 6. The method of claim 1, wherein the comparing includes comparing the output signal to a reference voltage using a comparator of the temperature information circuit to provide the indication of temperature.
 7. The method of claim 1, wherein the comparing the output signal to the reference voltage includes comparing an output signal of a differential amplifier of the temperature information circuit with the reference voltage.
 8. The method of claim 7, wherein comparing the output signal of a differential amplifier of the temperature information circuit to a reference voltage includes receiving the reference voltage from a reference resistor.
 9. The method of claim 7, wherein comparing the output signal of a differential amplifier of the temperature information circuit to a reference voltage includes receiving the reference voltage from a reference diode.
 10. The method of claim 1, including receiving the reference voltage from a reference generator of the temperature information circuit.
 11. The method of claim 10, wherein the reference generator includes a band-gap reference circuit.
 12. The method of claim 10, wherein the reference generator includes a diode based reference circuit.
 13. The method of claim 10, wherein the receiving the reference voltage includes applying a voltage across a voltage divider to provide the reference voltage.
 14. The method of claim 13, wherein applying the voltage includes applying the voltage across a voltage divider including an external resistance.
 15. The method of claim 13, wherein the applying the voltage includes applying the voltage across a voltage divider including a programmable resistance to provide a programmable reference voltage. 